javascript - Why this loop backwards is much slower than going forward? -

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i have answer guy question here how count string occurrence in string? playing algorithms here, , after benchmarking functions wondering why backwards loop slower forward.

graph

benchmark test here

note: code below not work supposed be, there others work (thats not point of question), aware before copying>pasting it

forward

function occurrences(string, substring) {    var n = 0;   var c = 0;   var l = substring.length;    (var = 0, len = string.length; < len; i++) {      if (string.charat(i) == substring.charat(c)) {       c++;     } else {       c = 0;     }      if (c == l) {       c = 0;       n++;     }   }   return n; }

backwards

function occurrences(string, substring) {    var n = 0;   var l = substring.length - 1;   var c = l;    (i = string.length; > 1; i--) {      if (string.charat(i) == substring.charat(c)) {       c--;     } else {       c = l;     }      if (c < 0) {       c = l;       n++;     }   }   return n; }

i think backwards test has bug:

for (i = string.length; > 1; i--) {

should be

for (i = string.length - 1; >= 0; i--) {

when i string.length, string.charat(i) undefined. several thousand times, , yield substantial difference.

here's modified test seems yield closer identical performances.


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